1. Field of the Invention
The present invention relates to equipment for polishing both sides of a rectangular substrate, such as a glass substrate, a quartz substrate, a sapphire substrate, a GaAs substrate, or a silicon substrate, etc., simultaneously in order to planarize the substrate and reduce the thickness thereof, and a method to planarize both sides of the rectangular substrate. In particular, the double-sided polishing equipment for the rectangular substrate is typically used to polish both sides of a glass plate for LCD devices, between which liquid crystal is injected, a glass laminate for a flat panel display, or a glass substrate for a display device, within which electrodes are provided and between which liquid crystal is injected.
2. Description of the Related Art
Glass plate for LCD devices, between which liquid crystal is injected, or glass substrates for display devices, within which electrodes are provided and between which liquid crystal is injected, are known and used for LCD panels. (For example, see Japanese Unexamined Patent Application Publication 2003-255291, Japanese Unexamined Patent Application Publication 2004-21016, and Japanese Unexamined Patent Application Publication 2005-3845.)
Typically, the thickness of rectangular glass plate used for such LCD panels is reduced by grinding the surface or using a lapping process. Furthermore, its ground or lapped surface is planarized by an etching process or a polishing process performed on each side or on both sides at the same time.
Either a method of polishing both sides of the rectangular glass plate with polishing pads at the same time, or a method of separately polishing each side can be used. The double-sided polishing method has a carrier main body forming a gear part around the periphery and provides a pocket about the size and shape of the rectangular glass plate. The carrier main body has a supporting member placed between the flat edge of the rectangular glass plate and the perimeter part of the pocket provided in the carrier main body. The carrier main body is made from a high rigid material. Further, the carrier is typically made of a flexible material that is not prone to damaging the rectangular glass plate at least when the contact site of the supporting member of the glass plate with the rectangular glass plate is brought into contact with the rectangular glass plate. When the rectangular glass plate is supported by the carrier, a driving mechanism for the double-sided polishing equipment will rotate the carrier by means of a gear part on the carrier main body to rub both sides of the rectangular glass with a pair of round polishing pads that are coaxial in order to polish both sides of the rectangular glass plate. (For example, see Japanese Unexamined Patent Application Publication H6-218667.)
As a method of polishing LCD devices, another manufacturing method is suggested in which a spacer member is provided on one glass substrate on which a driver for driving liquid crystals is to be fitted so as to polish liquid crystal cells after the processing vertical and horizontal dimensions of liquid crystal cells. A pair of rectangular glass substrates in a product size are rubbed with a pair of round polishing pads provided coaxially at centers of axes of the polishing heads on both sides of the liquid crystal cell (rectangular glass plate) in order to make the liquid crystal cell thinner. (For example, see Japanese Unexamined Patent Application Publication 2003-255291.)
As a method of polishing each side of a large rectangular glass plate with the polishing pad, a polishing method for a rectangular glass plate is suggested, including a process of putting a rectangular glass plate into a film frame where the film on which a rectangular glass plate can be applied is applied. The method includes attaching the frame to the carrier or a process of attaching the film frame where the film on which a rectangular glass plate can be applied is applied onto the carrier. The method further includes applying the rectangular glass plate onto the film frame and a process of polishing by moving the carrier on which the film frame is attached and the polishing pad closer to each other. The method further includes pressing the surface to be polished of the rectangular glass plate applied on the film onto the polishing pads, and a process of, after polishing the rectangular glass plate, removing the film frame from the carrier and then the rectangular glass plate from the film frame or a process of, after polishing the rectangular glass plate, removing the rectangular glass plate from the film frame and then the film frame from the carrier. (For example, see Japanese Unexamined Patent Application Publication 2004-122351.)
The method of polishing each side of a rectangular glass plate has the advantage that the rectangular glass plate hardly deviates from the polishing equipment during polishing. However, polishing each side separately requires more polishing-process stages as well as a procedure to turn over the rectangular glass plate halfway through the process, so polishing equipment becomes more bulky than double-sided polishing equipment that can polish both sides of a rectangular glass plate at the same time. In other words, single-sided polishing equipment requires a big footprint, which is a disadvantage.
Although double-sided polishing equipment has the advantage of shorter polishing time than is necessary for the method of polishing each side separately, there is a concern that, while polishing, the rectangular glass plate within the carrier may deviate from the polishing equipment if the substrate is thin, with differences in thickness of up to 1 mm.